The safe transmission of data is of great significance particularly in motor vehicles because control of safety-related systems such as airbags or automatic braking systems must operate safely.
As a rule, the data to be transmitted in modern motor vehicles are present in digital form and their transmission is controlled and monitored by microcontrollers. The digital data are usually transported via bus systems from a transmitter to one or more receivers which interconnect the various systems with one another in the car. For example, the CAN (Controller Area Network) bus or the TTCAN (Time Triggered CAN) bus, respectively, the LIN (Local Interconnect Network) bus, Ethernet or the FlexRay bus are used.
Apart from the operational reliability which has the aim, e.g. that the data to be transmitted by a transmitter are not changed by unintentional disturbances, e.g. short circuits on the transmission line, and are therefore not received faultlessly at the receiver, protection against malicious attacks must also be ensured.
One example of a malicious attack by a hacker in the case of a car could be to interfere with the internal bus system of the vehicle and to falsify the transmitted data. An attack could also consist not in changing the data themselves but in interrupting, delaying or recording for later purposes the data traffic on the bus system.
A transmission of digitally present user data from a transmitter to a receiver is carried out, for example in the form of data blocks or data frames which, apart from the user data, contain further data which, among other things, contribute to discovering and/or correcting disturbances in the transmission. These further data are generated by coders which generate code words for protecting the user data on the basis of input data, supplied to them, within a particular time. The code words are transmitted in the form of code blocks in addition to the user data blocks.
The data frames which are produced from user data blocks and code blocks must not have an arbitrary length as the maximum block or frame length is specified by the various communication standards or bus systems. In addition, user data blocks and code blocks must not be modified in such a manner that such a malicious intervention is not detectable.
German patent specification DE102010042539B4 shows a data transmitter for transmitting blocks of user data which uses an encryption device and an extractor. In this context, only a part of the result of the encryption is appended to the user data before the transmission.
International patent application WO 2013/128317 shows a method and a system for measures against a repeated transmission of recorded messages at a CAN bus by using counts. These counts indicate the number of messages hitherto transmitted.
It is the object of the present invention to provide a method and a system by means of which a high measure of data security is achieved during data transmission, especially in a motor vehicle.